1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the zoom lens. The zoom lens may be particularly suitable for use in an image pickup apparatus such as a digital still camera, a video camera, a monitoring camera, a broadcasting camera, and a film camera.
2. Description of the Related Art
The zoom lens used for an image pickup apparatus equipped with a solid-state image sensor, such as a digital still camera, a video camera, and a monitoring camera, is required to have the entire zoom lens being compact with a wide angle of view, a high zoom ratio, and high optical performance.
As an example of a zoom lens for addressing the above-mentioned requirements, Japanese Patent Applications Laid-Open Nos. 2010-181787, 2010-54722, and 2007-72263 discuss a four-unit zoom lens including four lens units having negative, positive, negative, and positive refractive power, respectively, in order from an object side to an image side.
The zoom lens discussed in Japanese Patent Application Laid-Open No. 2010-181787 has a focal length of 25.5 mm at the wide-angle end converted for a 35 mm silver-halide camera and a zoom ratio of around 6.7. The zoom lens discussed in Japanese Patent Application Laid-Open No. 2010-54722 has a focal length of 21.0 mm at the wide-angle end converted for a 35 mm silver-halide camera and a zoom ratio of around 4.8. The zoom lens discussed in Japanese Patent Application Laid-Open No. 2007-72263 has the focal length of 34.5 mm at the wide-angle end converted for a 35 mm silver-halide camera and a zoom ratio of around 2.9.
In order to realize a wide angle of view in a negative lead type zoom lens, in which a lens unit closest to the object side has negative refractive power, the front lens diameter increases. In addition, to realize a high zoom ratio, the amount of movement needs to be increased in each lens unit, which accordingly increases the total lens length.
In order to realize a wide angle of view and a high zoom ratio while reducing the total lens length, the refractive power of each lens unit may be increased to reduce the number of lenses in each lens unit. However, the resulting zoom lens has a large variation of aberration caused by zooming, and accordingly, it becomes difficult to obtain high optical performance for the entire zooming range.
In order to realize a negative lead type zoom lens of compact size with a wide angle of view, a high zoom ratio, and high optical performance, it is necessary to set the refractive power and the lens configuration of each lens unit appropriately.
Here, the zoom lenses discussed in Japanese Patent Application Laid-Open Nos. 2010-181787, 2010-54722, and 2007-72263 do not sufficiently realize both of the wide angle of view and high zoom ratio.